Does DNA stay open during transcription?

• A. Yes
• B. No, it closes after initiation
• C. Only in Eukaryotes
• D. Only in Prokaryotes

Answer: (B)

Transcription needs a temporary open region of DNA to expose the template strand, but this unwinding is not kept open as the enzyme moves along. RNA polymerase creates a short transcription bubble, about 10–15 base pairs, where the DNA is unwound to read the template and synthesize RNA. As elongation proceeds, the DNA behind the enzyme re-forms the double helix, so after initiation the region behind the polymerase is closed again. The bubble ahead remains briefly unwound, but the overall pattern is transient unwinding rather than a permanently open DNA duplex. Topoisomerases help manage the extra twisting (supercoiling) that results from opening and moving along the DNA.

So the best choice reflects that the DNA does not stay open after initiation. Both prokaryotes and eukaryotes share this transient opening, though chromatin structure in eukaryotes adds complexity to access.